This disclosure relates generally to ring oscillator circuits, and more particularly to testing of a ring oscillator with a power sensing resistor.
Ring oscillators are analog circuits including of an odd number of inverting stages connected in series that may be used for timing purposes. A ring oscillator may be designed to have a particular frequency of oscillation, and may be attached to chip input/output (I/O) or embedded in chip circuitry to make the ring oscillator system-accessible for various purposes in a computing system.
In order to test a ring oscillator, off-chip analog test equipment may be used to measure the frequency of the ring oscillator. However, use of analog test equipment for ring oscillator testing may be relatively inaccurate and inefficient, especially for ring oscillators having a frequency in a relatively high range, due to the loading effect of test buffers that are inserted into the ring oscillator during such testing. For example, a test buffer may be connected at the ring oscillator output, and additional test buffers may be added at the output of each inverting stage of the ring oscillator to determine characteristics of the individual inverting stages. The presence of the test buffers may introduce a significant load on the ring oscillator, rendering the testing of the ring oscillator inaccurate. Such ring oscillator testing disturbs the ring oscillator by adding extra load to the ring oscillator circuit, which slows down the oscillating frequency and stage delay of the ring oscillator. Inaccurate testing results cause difficulty in correlation of the impact of ring oscillator manufacturing process parameters to ring oscillator performance.